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Backport PR #49839 on branch 1.5.x (PERF: Fix performance regression in isin for empty values) #49860

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Merged
merged 1 commit into from
Nov 23, 2022
Merged

Backport PR #49839 on branch 1.5.x (PERF: Fix performance regression in isin for empty values) #49860

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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.5.3.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ including other versions of pandas.

Fixed regressions
~~~~~~~~~~~~~~~~~
-
- Fixed performance regression in :meth:`Series.isin` when ``values`` is empty (:issue:`49839`)
-

.. ---------------------------------------------------------------------------
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2 changes: 2 additions & 0 deletions pandas/_libs/lib.pyx
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Expand Up @@ -1480,6 +1480,8 @@ def infer_dtype(value: object, skipna: bool = True) -> str:
else:
if not isinstance(value, list):
value = list(value)
if not value:
return "empty"

from pandas.core.dtypes.cast import construct_1d_object_array_from_listlike
values = construct_1d_object_array_from_listlike(value)
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6 changes: 5 additions & 1 deletion pandas/core/algorithms.py
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Expand Up @@ -465,7 +465,11 @@ def isin(comps: AnyArrayLike, values: AnyArrayLike) -> npt.NDArray[np.bool_]:
orig_values = values
values = _ensure_arraylike(list(values))

if is_numeric_dtype(values) and not is_signed_integer_dtype(comps):
if (
len(values) > 0
and is_numeric_dtype(values)
and not is_signed_integer_dtype(comps)
):
# GH#46485 Use object to avoid upcast to float64 later
# TODO: Share with _find_common_type_compat
values = construct_1d_object_array_from_listlike(list(orig_values))
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